全文获取类型
收费全文 | 457603篇 |
免费 | 46175篇 |
国内免费 | 243篇 |
出版年
2018年 | 9205篇 |
2017年 | 9106篇 |
2016年 | 8443篇 |
2015年 | 6449篇 |
2014年 | 7258篇 |
2013年 | 10835篇 |
2012年 | 14288篇 |
2011年 | 18957篇 |
2010年 | 13728篇 |
2009年 | 13028篇 |
2008年 | 16452篇 |
2007年 | 18089篇 |
2006年 | 10918篇 |
2005年 | 11306篇 |
2004年 | 10768篇 |
2003年 | 10648篇 |
2002年 | 10385篇 |
2001年 | 18992篇 |
2000年 | 19253篇 |
1999年 | 15488篇 |
1998年 | 5426篇 |
1997年 | 5699篇 |
1996年 | 5510篇 |
1995年 | 4994篇 |
1994年 | 5113篇 |
1993年 | 5002篇 |
1992年 | 12919篇 |
1991年 | 12352篇 |
1990年 | 12271篇 |
1989年 | 12242篇 |
1988年 | 11137篇 |
1987年 | 10601篇 |
1986年 | 9818篇 |
1985年 | 9857篇 |
1984年 | 8002篇 |
1983年 | 6968篇 |
1982年 | 5299篇 |
1981年 | 4666篇 |
1980年 | 4547篇 |
1979年 | 7660篇 |
1978年 | 5928篇 |
1977年 | 5290篇 |
1976年 | 5113篇 |
1975年 | 5538篇 |
1974年 | 5778篇 |
1973年 | 5700篇 |
1972年 | 5676篇 |
1971年 | 5018篇 |
1970年 | 4035篇 |
1969年 | 3732篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
232.
233.
A microcomputer mainframe linked system is described which allows video camera data capture and storage of one-dimensional whole-cell protein electrophoresis gel images, processing of normalized traces to produce a similarity matrix, and analysis of the matrix using the commercial cluster analysis program CLUSTAN. A new similarity coefficient is introduced which takes into account both band position and intensity. Forty-five strains of Haemophilus influenzae, including the eight biotypes and six serotypes, were analyzed using this system. Results demonstrated groupings which are consistent with known genetic relationships. 相似文献
234.
L E Taplin J P Loveridge 《Comparative biochemistry and physiology. A, Comparative physiology》1988,89(3):443-448
1. Nile crocodiles, reared in fresh water and exposed acutely to seawater, suffer marked dehydration and hypernatraemia. Cloacal urine osmolarity and potassium concentration increased markedly but urine sodium remains low. 2. Hypernatraemia is increased when secretion from the lingual salt glands is prevented. 3. C. niloticus appears not to drink seawater. 4. Similarities in osmoregulatory response between estuarine and Nile crocodiles suggest that the lingual salt glands of C. niloticus are functional in salt water, playing an important role in sodium balance. 5. Significant differences in the function of the renal/cloacal complex of Alligator and Crocodylus emphasize further the differences between these two groups of crocodilian and provide support for the postulated marine ancestry of many or all of the Crocodylidae. 相似文献
235.
Data are presented to show how the number and growth of juvenile salmon in streams in the Scottish Highlands are influenced by various physical (temperature, water chemistry, depth and velocity, type of substratum) and biotic (food resources, competition, recruitment) factors. 相似文献
236.
EMMA DESPLAND MARIA GUNDERSEN SIMON P. DAOUST BRIAN J. MADER NATHALIE DELVAS PAUL J. ALBERT ERIC BAUCE 《Physiological Entomology》2011,36(1):39-46
The pattern of feeding of Eastern spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera, Tortricidae) is compared on foliage from white spruce Picea glauca (Moench) Voss. (Pinaceae) trees previously determined to be susceptible and resistant to defoliation by budworm. No differences are observed in electrophysiological responses from taste sensilla to aqueous extracts of the two foliage types, nor is there a preference for either extract type in a choice test. Acetone extracts from the two foliage types are both preferred to a control sucrose solution, although neither elicits a preference relative to the other. These results suggest that there is no difference in phagostimulatory power of internal leaf contents of the two foliage types. Longer‐term observation of feeding behaviour in a no‐choice situation shows no difference in meal duration, confirming the lack of difference in phagostimulatory power. However, on average, intermeal intervals are twice as long on the resistant foliage, leading to an overall lower food consumption during the assay. This result suggests an anti‐digestive or toxic effect of the resistant foliage that slows behaviour and limits food intake. Previous research has shown that waxes of the resistant foliage deter initiation of feeding by the spruce budworm and that this foliage contains higher levels of tannins and monoterpenes. The data suggest that the resistant foliage contains a post‐ingestive second line of defence against the spruce budworm. 相似文献
237.
Effects of antimicrotubular agents in cAMP production and in steroidogenic response of isolated rat Leydig cells 总被引:1,自引:0,他引:1
D Saltarelli M P De la Llosa-Hermier C Tertrin-Clary C Hermier 《Biology of the cell / under the auspices of the European Cell Biology Organization》1984,52(3):259-266
In dispersed rat Leydig cells, colchicine was found to stimulate basal cAMP production and testosterone secretion in a dose and time-dependent manner, but to a lesser extent than LH. However, these drugs are unable to stimulate adenylate cyclase activity in plasma membranes isolated from these cells. The amount of testosterone secreted at 150 min under the influence of colchicine and LH added simultaneously was not different from the amount produced during stimulation by LH alone. It is only after exposure of the cells for 1 hr to colchicine that the accumulation of cAMP in response to LH was inhibited; furthermore, both intracellular and medium testosterone accumulation in response to the hormone were reduced. Similar effects were observed with two other alkaloids, vinblastine and podophyllotoxin. The three drugs also inhibited the stimulation of testosterone secretion by 8-Br-cAMP or choleratoxin. These studies suggest that the state of microtubule polymerization and/or tubulin can influence the process of steroidogenesis in rat Leydig cells. 相似文献
238.
C Julien C Barres P Kandza J Sassard 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1989,308(8):219-222
Intra-aortic blood pressure (BP) was measured in conscious rats after early chronic destruction of the peripheral sympathetic nervous system (SNS) with guanethidine. In sympathectomized rats, the mean level of BP was not different from that of control rats but its variability was markedly increased. These results indicate that functional integrity of the SNS is of primary importance for the short-term control of BP but is not essential for its long-term maintenance. 相似文献
239.
Summary Amylase, dehydrogenase, arylsulphatase and phosphatases activities were measured in a clay-loam soil amended with seven different
crop residues. All enzyme activities, except phosphomonoesterase, were generally higher in the derived soil samples than in
the original soil. Addition of tobacco and sunflower residues caused an increase on most of the enzyme activities while tomato
residues increased only the amylase and phosphodiesterase activities.
As the enzyme activities were positively correlated to each other, a common source of the enzymes is suggested even though
the coefficients of correlation demonstrate that only a low percentage of the variability can be ascribed to the interactions
among enzyme activities. 相似文献
240.